Applicant: The applicant, Dr. Yuri E. Nesmelov, is a physicist whose research has focused on the interaction of electromagnetic fields with matter. Dr. Nesmelov proposes to learn and utilize molecular biophysical and biochemical techniques to round out a multidisciplinary approach to be used in studying myosin functional dynamics. Career Development/Training Plan: The primary element of the plan will be the acquisition of advanced molecular biophysical and biochemical techniques from mentored training. The majority of the training will come from the primary mentor, Dr. David D. Thomas, who is an internationally known scientist in the field of muscle biophysics, and is the director of an NIH-funded training program in muscle research. Additional training in cell and molecular biology will be provided by the co-mentor, Dr. Margaret Titus, who is well known for her work on myosin. Part of the research (W band electron paramagnetic resonance (EPR)) will be performed with a collaborator, Dr. Peter Fajer, a renowned specialist in biological EPR and muscle biophysics. Structured activities for further career and research development will include attendance and participation at national scientific meetings, regular involvement in journal clubs and seminars, and affiliation with the Muscular Dystrophy Center at the University of Minnesota. Research Plan: The overall aim of this proposal is for Dr. Nesmelov to learn molecular biophysical and biochemical techniques and apply them together with site-directed spin labeling and multifrequency EPR spectroscopy, to explore internal dynamics of myosin motor functioning. The proposed work is based on recent developments by the applicant in sensitivity improvement for EPR measurement, especially for experiments on myosin in solution, and in multifrequency EPR data analysis, to accurately characterize the dynamics of a protein- bound spin label. This approach will be used to obtain detailed information about the dynamic rearrangement of protein structural elements. These methods will be developed further, and used to define the kinetics of structural rearrangements of the relay helix and SH1 helix in myosin during the actomyosin ATPase cycle.